The present invention relates to crystalline polymorphic forms of atorvastatin hemi-calcium and novel processes for preparing crystalline solids.
Atorvastatin, ([R-(R*,R*)]-2-(4-fluorophenyl)-xcex2,xcex4-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenylamino)carbonyl]-1H-pyrrole-1-heptanoic acid), depicted in lactone form in formula (I) and its calcium salt of formula (II) are known in the art, and described, in U.S. Pat. No. 4,681,893, 5,273,995, and in commonly-assigned, co-pending U.S. Ser. No. 60/166,153, filed Nov. 17, 2000, all of which are herein incorporated by reference. 
Atorvastatin is a member of the class of drugs called statins. Statin drugs are currently the most therapeutically effective drugs available for reducing low density lipoprotein (LDL) particle concentration in the blood stream of patients at risk for cardiovascular disease. A high level of LDL in the bloodstream has been linked to the formation of coronary lesions which obstruct the flow of blood and can rupture and promote thrombosis. Goodman and Gilman, The Pharmacological Basis of Therapeutics 879 (9th ed. 1996). Reducing plasma LDL levels has been shown to reduce the risk of clinical events in patients with cardiovascular disease and patients who are free of cardiovascular disease but who have hypercholesterolemia. Scandinavian Simvastatin Survival Study Group, 1994; Lipid Research Clinics Program, 1984a, 1984b.
The mechanism of action of statin drugs has been elucidated in some detail. They interfere with the synthesis of cholesterol and other sterols in the liver by competitively inhibiting the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase enzyme (xe2x80x9cHMG-CoA reductasexe2x80x9d). HMG-CoA reductase catalyzes the conversion HMG to mevalonate, which is the rate determining step in the biosynthesis of cholesterol, and so, its inhibition leads to a reduction in the concentration of cholesterol in the liver. Very low density lipoprotein (VLDL) is the biological vehicle for transporting cholesterol and triglycerides from the liver to peripheral cells. VLDL is catabolized in the peripheral cells which releases fatty acids which may be stored in adopcytes or oxidized by muscle. The VLDL is converted to intermediate density lipoprotein (IDL), which is either removed by an LDL receptor, or is converted to LDL. Decreased production of cholesterol leads to an increase in the number of LDL receptors and corresponding reduction in the production of LDL particles by metabolism of IDL.
Atorvastatin hemi-calcium salt trihydrate is marketed under the name LIPITOR by Warner-Lambert Co. Atorvastatin was first disclosed to the public and claimed in U.S. Pat. No. 4,681,893. The hemi-calcium salt depicted in formula (II) is disclosed in U.S. Pat. No. 5,273,995. The ""995 patent teaches that the hemi-calcium salt is obtained by crystallization from a brine solution resulting from the transposition of the sodium salt with CaCl2 and further purified by recrystallization from a 5:3 mixture of ethyl acetate and hexane.
The present invention provides a new crystal form of atorvastatin hemi-calcium. The occurrence of different crystal forms (polymorphism) is a property of some molecules and molecular complexes. A single molecule, like the atorvastatin in formula (I) or the salt complex of formula (II), may give rise to a variety of solids having distinct physical properties like melting point, X-ray diffraction pattern, infrared absorption fingerprint and NMR spectrum. The differences in the physical properties of polymorphs result from the orientation and intermolecular interactions of adjacent molecules (complexes) in the bulk solid. Accordingly, polymorphs are distinct solids sharing the same molecular formula yet having distinct advantageous and/or disadvantageous physical properties compared to other forms in the polymorph family. One of the most important physical properties of pharmaceutical polymorphs is their solubility in aqueous solution, particularly their solubility in the gastric juices of a patient. For example, where absorption through the gastrointestinal tract is slow, it is often desirable for a drug that is unstable to conditions in the patient""s stomach or intestine to dissolve slowly so that it does not accumulate in a deleterious environment. On the other hand, where the effectiveness of a drug correlates with peak bloodstream levels of the drug, a property shared by statin drugs, and provided the drug is rapidly absorbed by the GI system, then a more rapidly dissolving form is likely to exhibit increased effectiveness over a comparable amount of a more slowly dissolving form.
Crystalline Forms I, II, III and IV of atorvastatin hemi-calcium are the subjects of U.S. Pat. Nos. 5,969,156 and 6,121,461 assigned to Warner-Lambert and crystalline atorvastatin hemi-calcium Form V is disclosed in commonly-owned, co-pending application Ser. No. 09/714,351. There is an assertion in the ""156 patent that Form I possesses more favorable filtration and drying characteristics than the known amorphous form of atorvastatin hemi-calcium. Although Form I remedies some of the deficiencies of the amorphous material in terms of manufacturability, there remains a need for yet further improvement in these properties as well as improvements in other properties such as flowability, vapor impermeability and solubility. The discovery of a new crystalline polymorphic form of a drug enlarges the repertoire of materials that a formulation scientist has with which to design a pharmaceutical dosage form of a drug with a targeted release profile or other desired characteristic.